1. Field of the Invention
The present invention relates to a method of forming a compound semiconductor layer, by a vapor phase growth of compound semiconductor thin-film using the hydrides and the organic metals as a raw material. In particular, the present invention relates to a method of preparing a compound semiconductor fitted for the planarization of the growth layer and the controlling of the deposit on a protective film used in a selective growth.
2. Description of the Related Art
For the purpose of improving the performance of a compound semiconductor device, a device using a two-dimensional gas or a quantum effect device has been energetically developed. It has been needed to control a growth speed precisely in the preparation of these devices, and a molecular-beam epitaxial growth (hereinafter referred to as MBE) method or a metal-organic vapor phase epitaxial growth (hereinafter refer to as MOVPE) method have been usually used. Actually, a steep hetero-junction interface has been formed in an atom-layer level by using these growth methods.
In case of the application of these structures to a device, a planarization of the hetero-junction interface will have a great influence on the characteristics of a device. For example, in a compound interface containing aluminum, a migration distance of the compound molecules containing aluminum is short, then the planarization will not be well effected. This poses such a problem that an electron mobility in the interface will be deteriorated. Recently, a selective growth method has been employed so as to more optimize a device structure. The merits of the selective growth method are that a high-quality selective growth region can be obtained and also a high-performance device can be obtained, as a damageless and comparatively low-temperature process can be realized thereby. In general, the selective growth has been carried out by MOVPE method, because it has been very difficult by MBE method.
However, in a process of the selective growth, there will arise many difficulties in the growth condition, the mixed-crystal ratio, the mask width and so on, in order not to deposit any polycrystals on a protective film. Especially in case of the compound containing aluminum, the more the mixed-crystal ratio of aluminum is raised and the higher the mask width is, the more polycrystals will be deposited on a protective film, thereby bringing about a problem that a desired device structure can not be obtained.